<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    *{
      margin: 0;
      padding: 0;
      list-style: none;
    }
    .box{
      width: 340px;
      height: 30px;
      background: url('imgs/bg.jpg') no-repeat center;
      margin: 30px auto;
      line-height: 30px;
    }
    .box .menu{
      float: left;
      width: 100px;
      height: 30px;
      background: url('imgs/libg.jpg') no-repeat center;
      text-align: center;
      margin-left: 10px;
    }
    .menu li{
      background: url('imgs/libg.jpg') no-repeat center;
    }
    .menu ul{
      display: none;
    }
  </style>
</head>
<body>
  <ul class="box">
    <li class="menu">一级菜单1
      <ul>
      <li>一级菜单11</li>
      <li>一级菜单11</li>
      <li>一级菜单11</li>
    </ul>
  </li>
    <li class="menu">二级菜单2
      <ul>
      <li>二级菜单21</li>
      <li>二级菜单21</li>
      <li>二级菜单21</li>
    </ul>
  </li>
    <li class="menu">三级菜单3
      <ul>
      <li>三级菜单31</li>
      <li>三级菜单31</li>
      <li>三级菜单31</li>
    </ul>
  </li>
  </ul>
  <script src="../../jquery-1.12.4.min.js"></script>
  <script>
    $('.menu').mouseenter(function(){
      $(this).children('ul').show()
    });
    $('.menu').mouseleave(function(){
      $(this).children('ul').hide();
    });
  </script>
</body>
</html>